Shoppers were plagued by flying ants - and more are on their way over the next few days - as swarms of the insects emerge as part of their mating ritual.
Readers of The Star reported thousands of ants crawling and flying across the city centre and in suburbs yesterday.
Shoppers and workers were brushing them off as the creepie crawlies flew around the city centre.
The story is the same all over the country as the ants emerge at roughly the same time nationwide to form new colonies.
Alistair McLean, curator of natural sciences for Museums Sheffield’s weather station at Weston Park, has been researching the ants for three years.
He said: “I have been collecting emergence data about when they come out each year and what the weather conditions are at the time.
“They have surfaced already this year. We had a bout at the beginning of July, one last week, and we are having a fairly major, substantial, emergence today.
“What we do know is the queens and drones emerge to go and mate.
“The males will go and die, then the females and queens will create new nests and go back under the stones.
“It should all be over in a couple of days.
“Nobody really knows why they all come out at the same time, so that’s why I started making notes to see if I can find out.
“Chances are it is something to do with weather, either temperature or pressure.
“There does seem to be a link with rainfall as well.”
Readers of The Star on Facebook reported flying ants in Shiregreen, Woodhouse, High Green, Gleadless, Westfield, Hackenthorpe and Thrybergh.
Victoria Hindle said there were ‘hundreds down at Victoria Quays’.
Sharon Savage wrote: “There are some on my washing in Fox Hill.”
And Lynn Carnall said: “Just been to Asda in Handsworth and there was a plague of them outside the entrance. Horrible things.”